This invention relates to duplexers of the type used for satellite antennas.
Typically, a satellite antenna comprises a cluster or array of individual horns positioned to direct individual radio frequency beams onto a reflector which redirects a combined beam to the desired coverage area of the earth.
A feed network for the satellite antenna comprises a transmit network, a receive network and a duplexer array (also known as a diplexer) the purpose of which is to allow the transmit and receive networks to share the same array of horns by separating the transmit signals from the receive signals.
A conventional duplexer for K-band operation (14/12 GHz) is realized using waveguide WR75. The duplexer comprises a transmit filter and a receive filter connected together in generally a V configuration to form a common port for connection to the horn array and separate transmit and receive ports. Each filter is typically a 4-pole Chebyshev design, with direct coupling between resonators. The coupling elements are inductive irises soldered to the waveguide body and spaced apart approximately a half wavelength. Tuning screws and coupling adjustment screws are employed to overcome the problem of dimensional tolerances in manufacture and to achieve the correct inter-cavity coupling and centre frequency.
The main disadvantages with this prior duplexer are, firstly, that it requires careful tuning on an individual basis and, secondly, it is relatively difficult to manufacture and does not lend itself readily to fabrication as part of a larger assembly.